This invention relates generally to the reprocessing of nuclear reactor fuel elements to recover the fissile material from spent fuel elements. particularly, the present invention is concerned with the dissolution of the fuel elements as the initial step in the separation and recovery of the fissile materials by liquid extraction techniques. More specifically, the invention concerns the dissolver vessel in which the fuel elements are dissolved into liquid solution and is directed toward an improved bottom assembly for the dissolver vessel.
As is well known in the art, spent nuclear reactor fuel elements are reprocessed in order to recover the valuable fissionable material for reuse as nuclear fuel. In the very commonly used liquid extraction techniques, the fuel elements are dissolved into solution for subsequent separation of the fissionable material from the fission products, cladding material, etc., and ultimate recovery of the fissionable material. At the head-end of such reprocessing schemes there is generally a dissolver vessel in which is carried out the initial step of dissolving the nuclear reactor fuel elements to place the materials in solution for the subsequent liquid extraction separation steps. A particular nuclear fuel reprocessing facility employing these techniques is the Idaho Chemical Processing plant located at the U.S. Atomic Energy Commission's Idaho National Engineering Laboratory, formerly named the National Reactor Testing Station, fissile southeastern Idaho. An understanding of fuel reprocessing and fissible material recovery systems in general and specifically the system in use at this reprocessing facility can be obtained from a more detailed discussion contained in AEC report No. IN-1471 entitled "Zirconium Fuel Reprocessing Campaign of 1960" , which report is incorporated herein by reference. While the particular reprocessing scheme described is concerned with zirconium-clad fuel, a similar system and similar equipment is used for the reprocessing of other types of fuel such as aluminumclad fuels. Other reprocessing schemes such as may be used at other facilities also employ similar equipment.
In these reprocessing schemes, the initial step is the introduction into a dissolver vessel of the spent nuclear reactor fuel elements. In order to eliminate unnecessary handling and the difficulty of mechanically lowering the fuel elements into the dissolver vessel, a dissolver vessel has been designed with a charging chute through which the fuel elements are dropped into the dissolver vessel. Prior to charging the dissolver vessel with the fuel elements, water, usually containing a nuclear poison for criticality considerations, is pumped into the dissolver vessel in order to cushion the fall of the fuel elements. However, since the fuel elements are typically dropped from a height of about 28 feet to the bottom of a dissolver vessel, it is necessary that the dissolver vessel be designed with a reinforced bottom to prevent the dropping fuel elements from damaging the integrity of the dissolver vessel. Dissolver vessels have therefore been designed with a sturdy flat bottom, commonly referred to as a crash plate, which permits the dropping of the fuel elements into the vessel.
During the dissolution of the fuel elements, some solids which do not dissolve in the dissolvent are deposited and accumulate in the dissolver vessel, principally falling to the bottom. Difficulties have been encountered in the presently used dissolver vessels in flushing these accumulated solids from the dissolver vessel. A sparging ring used to agitate the solids on the bottom to facilitate flushing from the vessel was found to be subject to damage by the impact from dropped fuel elements.
Consequently, it is an object of the present invention to provide an improved bottom assembly for a dissolver vessel for a nuclear reactor fuel reprocessing system.
It is another object of the present invention to provide a bottom assembly for a dissolver vessel which will permit agitation of accumulated solids, thus facilitating flushing of the solids from the vessel.